Since the April 20 explosion and fire that sank the BP Deepwater Horizon off-shore oil rig, about 800,000 liters of crude oil a day have been spewing from the broken well into the Gulf of Mexico.

The massive spill is threatening marine life, commercial fishing and hundreds of kilometers of coastal wetlands.

When President Barack Obama visited the Gulf region Sunday to assess the scope of the disaster and the steps being taken to end it, he made it clear to reporters what he sees as the top priority.

"We've got a bunch of different tasks. The first one is how do we plug this hole."

'The hole'

That hole - actually three gushing vents of crude oil at the damaged ocean-floor well-head nearly 2 kilometers below the surface - was caused by the failure of a blow-out preventer. That's a pressure-sensitive safety device designed to shut off the flow of oil in case of a sudden break in the pipe leading up to the floating oil platform.

Lamar McKay, head of BP America told ABC News that attempts to use underwater robotic equipment to fix the shut-off valve are complex. "This is like doing open-heart surgery at 5,000 feet [1,524 meters], in the dark with robot-controlled submarines."

British Petroleum is leading the repair and cleanup effort. Chief Executive Officer Tony Hayward says BP has also begun drilling a relief well to intersect the existing well, bore a hole in it, and then pump in cement to plug the leak. But that job could take as long as three months to complete.

Dome solution

Right now, the best hope for a quick fix appears to be the 12-meter tall concrete-and-steel domed tower that BP engineers are preparing to lower into the Gulf and place directly over the main leak possibly by week's end. The 80-ton box would capture and siphon the escaping oil to tankers on the surface.

Richard Charter is an oil industry expert and senior policy advisor for Defenders of Wildlife. He says the dome technique has never been used at such depths and is risky.

"I would hope that they would be very careful in deploying those with cables and remote operating vehicles, not to pump and break off the riser pipe." Because if that happens, he says, "You would have a wide open well on the sea floor and the flow rate could increase exponentially."

BP announced Wednesday that their robotic submersible had managed to stop one of the three leaks. However, until the other two are capped, oil continues to flow unabated into the Gulf of Mexico.

New approaches

The disaster response team includes U.S. government agencies and British Petroleum.

BP's Chief Executive Officer Tony Hayward says a massive operation is underway to contain the spreading oil slick down before it reaches shore.

"We're doing something that's never been done before, we're deploying dispersants on the sea bed at the source of the leak. On the surface we have a fleet of 100 vessels to contain the spill. We are dispersing dispersant from almost an air force of planes. We've got five planes including two Hercules C-130s deploying dispersant."

Those dispersants, designed to break the oil into small and more manageable globules, are not without their problems, says Defenders of Wildlife Senior Advisor Richard Charter.

"And some of it sinks as tar balls. So in the ocean the toxicity impacts the bio-availability of the oil toxins, and it may be greater as a result of applying the dispersant. But it may mean that fewer birds die in the marshes of Louisiana as the oil washes ashore."

Charter says such methods to contain or slow a spill - like dispersants, skimming boats and floating booms - have been around for decades.

He such methods will only address about 10 percent of the oil. "Even if you have containment booms deployed in the ocean, you quickly reach a certain sea state where the oil goes over the boom and under the boom and there is a component of this slick that is under the surface anyway and that just goes right under the boom."

Human factors

Robert Bea, an engineer with the Center for Catastrophic Risk Management at the University of California Berkley has worked on oil disaster teams for five decades.

He compares technology developed for off-shore drilling to that developed to send astronauts into space. Bea says the pattern of repeated failures on oil rigs - including this latest disaster - points to human factors and not prevention technology. "[Among these are] procedures, how people are selected, how they are trained at various levels. And I think that we are yet to see this kind of thinking show up strongly on board these drill rig operations."

Bea hopes the massive oil spill will prompt new and stricter regulations governing off-shore oil drilling operations. He says these rules should address not only technical fixes like requiring remote shut-offs, moving operations farther from shore, and better containment strategies, but also management issues like how a rig is staffed and operated.

Bea says the oil and gas industry has consistently opposed stricter federal regulation, most recently in 2009. Among the voices rejecting those rules, he says, was British Petroleum.

siphon: to move a liquid from one container to another, using a siphon 用虹吸管吸（或抽）

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（来源：VOA 编辑：陈丹妮）